In a power system, a surge arrester is provided to protect facilities from abnormal voltage (surge) due to thunderbolt. The surge arrester has a nonlinear resistor, for example, containing zinc oxide as a main component. The nonlinear resistor is insulative when normal voltage acts, and becomes conductive by decreasing in resistance value when abnormal voltage acts.
Among surge arresters, a polymer surge arrester is configured such that an electrode is placed at each of an upper end and a lower end of a stack made by stacking a plurality of nonlinear resistors and a plurality of insulating rods are arranged side by side around the outer peripheral surface of the nonlinear resistors. Further, in the polymer surge arrester, an outer skin made of insulating resin covers the outer peripheral surface of the stack of the nonlinear resistors around which the insulating rods are arranged. The insulating rod is formed using, for example, FRP (Fiber Reinforced Plastics), and the outer skin is formed using, for example, silicone rubber.
Since the polymer surge arrester is lower in mechanical strength than an insulator surge arrester housing the nonlinear resistors in a porcelain container and therefore needs to be improved in mechanical strength.
The polymer surge arrester has the outer skin formed of an insulating resin with low mechanical strength. Therefore, the polymer surge arrester needs to secure the mechanical strength of the whole polymer surge arrester by the insulating rods and the nonlinear resistors higher in mechanical strength than the outer skin.
However, it is sometimes not easy to sufficiently improve the mechanical strength in the polymer surge arrester. For example, when fastening is realized by attaching a male screw part provided at the insulating rod to a female screw part of the electrode, the male screw part provided at the insulating rod may break when a bending stress is applied to the polymer surge arrester. Further, the fastening may be loosened because thermal processing is performed when forming the outer skin is formed by molding the insulating resin.